RadioAstron Space-VLBI observation of SN2014J and the possible AGN in M82

ATel #6197; Kirill V. Sokolovsky (ASC Lebedev/SAI MSU), Petr A. Voytsik (ASC Lebedev), Alexei V. Alakoz (ASC Lebedev), Yoshiharu Asaki (JAXA), Uwe Bach (MPIfR), Roman Feiler (Torun), Marcin P. Gawronski (Torun), Marcello Giroletti (INAF IRA), Mikhail A. Kharinov (IAA), Alexander V. Ipatov (IAA), Alexander M. Kutkin (ASC Lebedev), Ismail A. Rahimov (IAA/Svetloe), Frank K. Schinzel (UNM), Pawel Wolak (Torun)
on 3 Jun 2014; 14:03 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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The Type Ia supernova SN2014J (ATel #5786, CBET #3792) appeared in M82 around 2014 January 14.75 UT (Zheng et al., arXiv:1401.7968). On 2014 March 27 05:20-06:00 UT (71.5d after explosion) it was observed with the RadioAstron Space-VLBI array consisting of the 10m Space radio telescope (Kardashev et al., 2013 ARep, 57, 153) operating simultaneously at 1.6 and 4.8 GHz, the Effelsberg 100m (observing at 4.8 GHz), Usuda 64m (1.6 GHz), Kalyazin 64m (1.6 and 4.8 GHz), Torun 32m (1.6 GHz), and Svetloe 32m (4.8 GHz) telescopes. No radio emission was detected at the position of SN2014J (ATel #5821) with 7 sigma upper limits on the correlated flux density of 3 mJy (Effelsberg-Svetloe projected baseline of 28 Megawavelength) 17 mJy (Effelsberg-RadioAstron, 2100 Megawavelength, 10.5 Earth diameters) at 4.8 GHz and 12 mJy (Kalyazin-Torun baseline, 7.2 Megawavelength) 33 mJy (Kalyazin-RadioAstron baseline, 750 Megawavelength) at 1.6 GHz. This is in agreement with the earlier radio non-detections of SN2014J reported in ATel #5804, #5812, #6149, #6153 and Perez-Torres et al. arXiv:1405.4702.

While no radio emission was found from SN2014J, the compact radio source 0951+699 (coinciding with the center of M82) located in the same beam as the SN is clearly detected on ground-ground baselines with a flux density of about 12 mJy (Effelsberg-Svetloe) and 62 mJy (Kalyazin-Svetloe; 7.8 Megawavelength) at 4.8 GHz and 90 mJy at 1.6 GHz (Kalyazin-Torun). The flux density values are similar to the ones obtained in October 2010 2.3/8.4 GHz VLBI observations by Pushkarev & Kovalev (2012 A&A, 544, A34; see http://astrogeo.org/vlbi_images/ ). The source 0951+699 is not detected on space-ground baselines. Assuming the Gaussian brightness distribution, we use the flux densities measured at Kalyazin-Svetloe and Effelsberg-Svetloe baselines to estimate the 4.8 GHz brightness temperature of 0951+699 to be of the order of 10^11 K in observer's frame. The observed brightness temperature is consistent with the AGN nature of this source. However, radio supernovae in the past have shown similar brightness temperature values hundreds of days past the explosion.

The nearby source 1022+707 was observed by the ground stations only to set the amplitude scale assuming the source has the flux density of 170 mJy at ground-ground baselines and flat spectrum. Considering the expected thermal noise level, the estimated coherence loss and the flux density of 0951+699 consistent with the previous measurements, we expect the amplitude on baselines with Kalyazin to be accurate to at least 50% (20% for other baselines).

Since phase referencing is challenging with the space antenna, a direct fringe detection experiment was attempted with two 20 minute-long scans on the position of SN2014J utilizing the full scan length for fringe search. The ground telescopes recorded two 16 MHz-wide sidebands in two orthogonal circular polarizations with 2-bit sampling at 256 Mbps while the space telescope utilized 1-bit sampling at 128 Mbps. The correlation was performed with the RadioAstron-enabled version of DiFX software correlator (Deller et al., 2011, PASP, 123, 275) developed by Anderson et al. (in prep.) installed at the ASC. The fringe search was performed with PIMA ( http://astrogeo.org/pima/ ).

The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the Russian Federal Space Agency, in collaboration with partner organizations in Russia and other countries. This work is based on observations with the 100-m telescope of the MPIfR at Effelsberg and radio telescopes of IAA RAS. We thank the RadioAstron mission, Alex Kraus, the PKE for approving and the staff of participating observatories for performing these observations.